Quark-lepton interchangeability at high energy:: [SU(3)]4 quartification -: art. no. 051301

We propose that quarks and leptons are interchangeable entities in the high-energy limit. This naturally results in the extension of [SU(3)](3) trinification to [SU(3)](4) quartification. In addition to the unbroken color SU(3)(q) of quarks, there is now also a color SU(3)(l) of leptons which reduces to an unbroken SU(2)(l). We discuss the natural occurrence of SU(2)(l) doublets at the TeV energy scale, which leads remarkably to the unification of all gauge couplings without supersymmetry. Proton decay occurs through the exchange of scalar bosons, with a lifetime in the range 10(34)-10(36) yr.